This invention relates generally to the art of random code generation, and more specifically concerns pseudo-random code generators which alter the output frequency spectrum of a pseudo-random bit generator to accomplish the pseudo-random code output.
Pseudo-random code generators of varying degrees of sophistication are well-known in the art. A common approach uses one or more shift registers with various combinations of feedback loops to provide a series of pseudo-random output bits. Since the bits are generated by a device operating on fixed feedback loop principles, the output of the device is only pseudo-random, i.e., the bit series will be repeated after a certain number of output bits have occurred. However, by selecting appropriate feedback combinations through special tables available in the art for a specified length of shift register, the random bit series may be quite extended. THe pseudo-random bit output of such devices using linear shift registers, however, occurs over a certain defined frequency spectrum. For different applications it may be desirable to change the frequency spectrum of the pseudo-random output. Conventional means for changing the output frequency spectrum of such a pseudo-random bit generator use output filters, although this technique has the significant disadvantage of distorting the square wave output so that it is no longer acceptable to drive follow-on logic circuits, or in other applications requiring a square wave signal.
In view of the above, it is a general object of the present invention to provide a pseudo-random code generator which overcomes the disadvantages of prior art code generators discussed above.
It is another object of the present invention to provide such a code generator which functions to shift the frequency spectrum of the output of a standard pseudo-random bit generator without distorting the waveform thereof.
It is a further object of the present invention to provide such a code generator which uses selected portions of the code generator output as feedback to influence the succeeding output of the code generator.
It is yet another object of the present invention to provide such a code generator in which the shift of frequency spectrum of the output of the code generator is controllable.